How to secure file uploads in PHP?

@lizzie 

File uploads can be a potential security risk for any web application. Therefore, it is important to take necessary measures to ensure that the uploaded files do not pose any security threat. Here are some tips to help you secure file uploads in PHP:

1. Limit file types: Restrict the types of files that can be uploaded to your server by specifying a list of acceptable file extensions. This will help prevent malicious users from uploading harmful scripts or executable files. You can use the "mime_content_type" function to determine the MIME type of the uploaded file.
2. Rename uploaded files: When a user uploads a file, rename it to a unique name that does not include the original file name. This will prevent users from overwriting existing files and will make it harder for malicious users to predict the file name.
3. Check file size: Set a maximum file size limit for uploads to prevent users from uploading excessively large files that can cause server performance issues.
4. Use server-side validation: Validate uploaded files on the server-side to ensure that they meet all necessary requirements. Check that the file has been successfully uploaded and that it is of the correct file type and size. You can use PHP's "is_uploaded_file" function to check if the file was uploaded via HTTP POST.
5. Store uploaded files outside of the web root: Store uploaded files in a directory that is outside of the web root directory. This will prevent users from accessing the uploaded files directly via a URL and will make it harder for malicious users to execute scripts.
6. Use secure file permissions: Set appropriate file permissions for uploaded files to ensure that only authorized users can access them. Use the chmod function to set file permissions.
7. Scan uploaded files for viruses: Scan uploaded files for viruses using an anti-virus scanner. This will help prevent users from uploading malicious files that can harm your server.

By implementing these measures, you can ensure that your file upload feature is secure and does not pose a risk to your web application.